Journal of Physical Chemistry vol:95 issue:9 pages:3771-3779
Anodic photocurrents are obtained upon excitation of xanthene dyes incorporated into Langmuir-Blodgett films deposited on SnO2. The observed quantum yield of the photocurrent strongly depends upon the applied electrode potential, the regenerator (hydroquinone) concentration, and the pH of the electrolyte. The photocurrent is nearly independent of the chemical structure of the dye or the amount of dye incorporated in the monolayer. For 3,6-bis(N-ethyl-N-octadecyl)aminoxanthylium perchlorate (PYR18) and N,N'-dioctadecylrhodamine 119 (RH18), the photocurrent action spectra resemble the absorption spectra of the mixed monolayer or a dilute solution of the dye in chloroform. Interactions between the chromophore and the cadmium arachidate matrix shift the spectral sensitization maximum of the surface-active bis(N-ethyl-N-octadecyl)rhodamine (RB18) to shorter wavelengths than the absorption maximum of the mixed monolayers or the action spectra of adsorbed rhodamine B. As observed for adsorbed rhodamine B the action spectra give no indication for the formation of sandwich dimers for RB18 and RH18. Analysis of Mott-Schottky plots obtained at low frequency indicates that decreasing the electrolyte pH leads to an anodic shift of the flat-band potential (E(fb)) and that the electrode is only partially covered by the deposited Langmuir-Blodgett film.